Irrigation Regime and Organic Fertilizers Influence on Oil Content and Fatty Acid Composition of Milk Thistle Seeds

Milk thistle (Silybum marianum L. Gaertn.) seeds contain relatively high amounts of edible oil. Influences of irrigation regime (full irrigation, moderate deficit, and severe deficit irrigation) and organic fertilizers (vermicompost [VM] and poultry manure [PM]) on the oil content and fatty acid (FA) composition of milk thistle seed were evaluated in a field trial. Averaged across treatments, seed oil content was 27% whereas unsaturated FAs constituted 78% of the oil composition. Linoleic acid (41.4%) and oleic acid (35.1%) were the most abundant unsaturated FAs whereas palmitic, stearic, arachidic, and behinic acids were major saturated FAs. Oil content was significantly influenced by irrigation regimes, but not by organic fertilizers. Severe deficit irrigation reduced oil content by 7.4% compared with full irrigation. Deficit irrigation had a minor effect on the FA composition of milk thistle oil where total unsaturated fatty acids (UFA) was lower in stressed plants. The application of soil organic amendments did not induce significant changes in unsaturated fatty acids but reduced the content of saturated ones which totally imposed positive effects on oil quality of milk thistle. According to the results, it seems that milk thistle has potential to be considered as an oil seed crop in low-input agricultural systems in arid and semiarid areas and moderate deficit irrigation can be implemented without deleterious effects on its oil content and quality.